Thanks to Jockie for pointing me in the right direction. I had the theme, and seemed to have the first two letters of the five-letter object, but this still left some intractable problems.
Turned out I had a valid but incorrect answer for 38A, a different African fruit which I'd found via Wikipedia (turned out it wasn't in Chambers but there seemed no need to check). My answer started with a K. Still a bit dubious about 'five cells in a straight line' which implies adjacent cells, but ho hum...all done now.